The ongoing cycle

learn how to find the area of a circle

November 17, 2009 at 6:31 am | Posted in Mathematics | 4 Comments
Tags: try to learn circles

Steps in finding the Area of a circle

Area of the circle

1. Figure out the length of the radius. This may be as simple as dividing the diameter by 2.
2. Note the formula. The formula for finding the area of a circle is:
3. Multiply the radius by itself to square it.
4. Multiply by pi.
   • If the instructions say “leave in terms of pi”, then just stick the pi onto your number.
   • If the instructions say anything about rounding, replace pi with 3.14 or use your calculator’s pi button.

Here is an example:

• Occasionally you will see a circle inside of a square. The side length of the square matches the diameter of the circle.
• Occasionally you may see a square inside of a circle. The diagonal of the square is also the diameter of the circle.

Finding the Area of a Sector

1. Find out how big the sector is in terms of degrees. Unfortunately, there is no set way to do this. It will vary considerably, depending on what information is being supplied in the problem, and it is not possible to include a step-by-step process for every situation.

   Circleparts.JPG

2. Create a fraction that has: the degrees from the sector’s central angle as the numerator, and 360° as the denominator.
3. Take the fraction down to lowest terms.
4. Figure out the radius of the circle.
5. Find the area of the circle (see previous section).
6. Multiply the fraction from step 3 with the area from step 5 OR divide the area by 360, then multiply by the # degrees in the partial circle.

Here is an example:

• Generally speaking, you will not get a whole number coefficient for pi. If your radius is a multiple of 3, you will get some kind of cancellation between the fraction and the results of the ( )², though. You will have to decide whether to: a) keep the fraction as a fraction and pi as pi, and cross-cancel as much as possible; or b) substitute 3.14 and finish the division completely.